1. Field of the Invention
The invention relates to separation processes and systems to remove or reduce impurities from unconventional and opportunity petroleum resources.
2. Description of the Related Art
Opportunity petroleum resources such as acidic crude oil, extra heavy oil, heavy oil, high salinity crudes, acidic residuum, gas oils, oil sand, diluted bitumen, and undiluted bitumen are typically treated to remove impurities such as asphaltenes, solids, sulfur, NSO, metals, chlorides, water, salts, and acids before sending the resource upstream for additional processing. One currently available treatment is solvent deasphalting (SDA). This process takes advantage of the fact that maltenes are more soluble in light of paraffinic solvents than asphaltenes. This solubility increases with solvent molecular weight and decreases with temperature. There are constraints with respect to how deep a SDA unit can cut into the residue or how much deasphalted oil (DAO) can be produced. Theses constraints are typically due to the DAO quality specifications required by downstream conversion units; and the final high-sulfur residual fuel oil stability and quality.
Solvent deasphalting has the advantage of being a relatively low cost process that has the flexibility to meet a wide range of DAO qualities. The process has very good selectivity for asphaltenes and metals rejection, some selectivity for carbon rejection and less selectivity for sulfur and nitrogen. It is best suited for the more paraffinic vacuum residues as opposed to the high asphaltenes, high metals, and high carbon containing vacuum residues. The disadvantages of the process are that it performs no conversion, produces a very high-viscosity byproduct pitch, and where high quality DAO is required, SDA is limited in the quality of feedstock that can be economically processed.
Delayed coking has been the preferred choice of many refiners for bottom of the barrel upgrading, due to the inherent flexibility of the process to handle highly contaminated residues. Delayed coking provides partial to complete conversion to naphtha and diesel, and almost complete rejection of carbon and metals. In the past, many cokers were designed to provide complete conversion of atmospheric residue to diesel and lighter, and today several cokers still operate in this mode. Most recently, cokers have been designed to produce heavy coker gas oil for catalytic upgrading, and minimize the production of coke. The economics of delayed coking are driven by the differential between transportation fuels and high-sulfur residual fuel oil. The yield slate for a delayed coker can be varied to meet a refiner's objectives through the selection of operating parameters. Coke yield and the conversion of heavy coker gas oil are reduced, as the operating pressure and recycle are reduced and to a lesser extent as temperature is increased. The disadvantages of delayed coking are that it is a thermal cracking process and it is a more expensive process than SDA although still less expensive than other conversion processes on heavier crudes. One common misconception of delayed coking is that the product coke is a disadvantage. Although coke is a low valued byproduct, compared to transportation fuels there is a significant worldwide trade and demand even for high-sulfur petcoke from delayed cokers as coke is a very economical fuel. In the past, most of the fuel coke produces in the U.S. has been exported to Europe and Japan, however, many of the coal burning power producers in the U.S. have now installed scrubbers and are now using or considering the use of petcoke as part of the fuel to their plant. In addition, there have been several 100% petcoke based power plants installed and many more are being considered. Several of these petcoke burning power plants utilize Foster Wheeler's Circulating Fluid-Bed Boiler Technology. In these plants a circulating bed of limestone captures the sulfur. One concern of the power producing companies in the U.S. has been “is there enough low value petcoke?”
One existing process integrates solvent deasphalting and delayed coking technologies. See, McGrath et al, “Upgrading Options for Heavy Crude Processing,” presented at AIChE Spring 1999 Meeting. The process purportedly provides synergistic application of the tow base technologies for increased liquid yield and energy utilization. The increased liquid yields are mainly attributable to the extraction of the high-valued DAO prior to coking. The heat integration between the solvent deasphalting and delayed coking sections features utilization of both high and low level coker waste heat sources in the SDA section. Removing the DAO fraction prior to delayed coking has two benefits. In the coking process this fraction is thermally cracked to extinction, degrading this material as an FCC feedstock. In addition, in thermally cracking this material to extinction, a significant portion will convert to coke. The process purportedly operates with deasphalted oil, both virgin and hydrotreated, and produces as much as 20 wt % coke at higher pressures and recycle rates. A delayed coker pilot plant has also been modified to operate on SDA pitch. This pilot plant has purportedly operated on feedstocks having ring and ball softening points as high as 295° F. With this process there is a significant reduction in byproduct fuel as compared to either solvent deasphalting or delayed coking. The operation can be tailored to meet the ability of a refinery to process a specific quantity or quality of cracking stock.
Production of usable hydrocarbons from unconventional and opportunity crudes has been the subject of much research since the oil crisis of 1973, and even before. The EIA has indicated there are 301.0 BBO of heavy oil and 531.0 BBO of bitumen currently recoverable in the Western Hemisphere. High acid crude processing (as a percent of total crude processed) is expected to grow from about 8.5% in 2004 to about 10.3% in 2009.
The traditional application of in situ production techniques involved drilling a well into the oil sands and extracting the bitumen almost as if it were conventional crude oil. The maturation of horizontal well technology and the development of steam assisted gravity drainage (SAGD) extraction techniques have revolutionized the in situ production industry. With the SAGD technology, two horizontal wells are drilled into the same reservoir, one directly above the other. Steam is injected into the top well, which heats up the surrounding tar-like bitumen and causes it to drain with the aid of gravity into the well bore of the lower well.
A separation train for producing and upgrading heavy oil and bitumen was reported by Kerr et al., “The Long Lake Project—The First Field Integration of SAGD and Upgrading,” Soc. Of Pet. Engrs., SPE/PS-CIM/CHOA, 2002 SPE International Thermal Operations and Heavy Oil Symposium and International Horizontal Well Technology Conference, Calgary, Alberta, Canada, 4-7 Nov. 2002 (hereinafter Kerr et al.). This publication describes a process for upgrading heavy oil and bitumen. The process produces a light, sweet synthetic crude from SAGD and an upgrading process that includes distillation combined with solvent deasphalting to partially upgrade bitumen and produce an asphaltenes by-product. The partially upgraded bitumen is then processed in a hydrocracker to produce what is termed a premium synthetic crude. The asphaltenes are fed to an asphaltenes gasification system to produce hydrogen for the hydrocracker and syn gas fuel for the SAGD process.
With the depletion of conventional oil supplies; bitumen extracted from oil sands has become a more attractive source of unconventional crude. The USA and Canada have the world's largest oil sand reserves, which are estimated to be 58.1 billion barrels and 1.6 trillion barrels, respectively. Bitumen contained in the oil sand is highly viscous with API gravities from 1 to 10. Bitumen is made up primarily of distillate and vacuum gas oil cuts in addition to contaminants such as solids, asphaltenes, carboxylic and other organic acids, salts, heteroatoms such as sulfur, nitrogen, and oxygen, and heavy metals. Bitumen must first be separated from the oil sand, and then upgraded before it can be used as a refinery feedstock.
The three major bitumen recovery technologies are surface mining, SAGD, and thermal treatment. SAGD is commercially proven and is used to recover bitumen that is not accessible by surface mining. However, SAGD requires large amounts of steam and is quite energy intensive. Thermal treatments such as vacuum pyrolysis are presently under investigation and development. This process produces less environmental pollution than the other two processes but consumes large amounts of energy. The surface mining process is widely used commercially.
Surface mining is currently used to recover bitumen from oil sands and includes process steps such as oil sands mining, bitumen extraction, and bitumen separation. The bitumen product is then sent to upgrading. Two major procedures for extraction and separation involves 1) water extraction, which uses hot water and caustic to wash and float the bitumen from the sand, and 2) organic solvent extraction, which employs an organic solvent to dissolve the bitumen from the surface of the oil sand. The disadvantages of the solvent extraction process are: environmental pollution due to the loss of solvent; storage of solvent inventories; large quantities of water are required to remove the solvent from the sand after extraction; and difficulties in process scale up.
In a currently practiced hot water extraction process oil sand is first washed by hot water and caustic to form a three-phase suspension made up of bitumen, water, and solids. The suspension (which may or may not also include an emulsion layer), which as been diluted with naphtha, enters a separation system involving gravity separation, flotation, centrifugation, and distillation where bitumen, solids, water, and naphtha are separated from each other. If the hot water extraction and the separation operations are successful, the bitumen product will contain very low concentrations of solids and water, and will be ready for downstream upgrading by coking or hydrocracking. A synthetic crude oil is produced by the upgrading process. However, various problems exist in the extraction and separation steps, which may lead to ineffective separation of the bitumen, solids, and water that may result in: large quantities of water usage and disposal in the tailings pond; environmental pollution; high energy consumption; unacceptable bitumen quality.
Available extraction and separation processes are encumbered with several problems. One problem is low bitumen extraction rate due to the existence of asphaltenes, salts, acids, and extra fine particles at the silica-water interface, and water-oil interface, the bitumen strongly adheres to the sand particles. The displacement efficiency of removing bitumen from the sand is low by hot water extraction alone. The remaining bitumen in the oil sand tailings is not only an issue with regard to bitumen yield, but also may be an environmental problem.
Emulsions present another problem. After the bitumen is displaced from the sand by hot water and caustic, a stable bitumen-water emulsion may form. The emulsion is stabilized by asphaltenes, salts, fine particles, and acids (specifically carboxylic and other organic acids with the previous referred to herein as naphthenic acids) at the bitumen-water interface. The emulsion is difficult to break by the conventional separation techniques in the existing process and will be either disposed o fin the tailings pond or carried over in the bitumen product. The emulsion that is carried over may cause serious problems in the downstream processes, such as corrosion, fouling, catalyst deactivation, and decreased operating efficiency.
Likewise, suspended fine particles smaller than 10 microns are very difficult to remove by flotation, gravity separation, or centrifugation. The fine particles are also responsible in part for formation and stabilization of emulsions, and will cause plugging problems in downstream processes. Fines may also prohibit bitumen droplet coalescence.
Furthermore, asphaltenes have higher aromaticity, low H/C molar ratio, high heteroatoms content (e.g. N, S, and O, commonly referred to as “NSO”), and contain heavy metals such as V and Ni. Asphaltenes have a higher molecular weight as compared with lighter petroleum fractions, and are the most difficult portion of the feedstock to upgrade. The dispersed colloidal asphaltenes particles play an important role in emulsion stabilization. Asphaltenes at the surface of bitumen droplets may also inhibit coalescence.
Additionally, heavy metals such as vanadium and nickel are normally associated with asphaltenes while NSO in the bitumen are associated with both resins and asphaltenes. Heavy metals may deteriorate catalyst activity in downstream operations, and may cause serious environmental problems if handled improperly. NSO are also important elements for air pollution generation. To remove some of these heteroatoms prior to Sox and Nox production would be beneficial. However, the processes discussed above typically do not remove the heavy metals or NSO contained in asphaltenes and resins. These contaminants are sent downstream with the bitumen for pollutant generation.
Carboxylic acids, commonly referred to as naphthenic acids, which are in the bitumen are another important surfactant to stabilize bitumen-water emulsions. These acids may also cause serious environmental pollution if released with water. Naphthenic acids, which are actually classified as resins, also contain a high level of heteroatoms. The current hot water extraction and separation process is not designed for naphthenic acid removal, except as salts which may contribute to emulsion stabilization.
The above problems are characteristic deficiencies of the current hot water extraction technology. In order to solve the problems, an effective and efficient bitumen extraction, separation, and upgrading technology needs to be developed.
U.S. Pat. No. 6,357,526 (Abdel-Halim, et al.), discusses field upgrading of heavy oil and bitumen. Additionally, the following patents assigned to Ormat, Inc., are related to deasphalting technology: U.S. Pat. Nos. 5,804,060; 5,814,286; 5,843,302; 5,914,010; 5,919,355; 5,944,984; 5,976,361; 6,183,627; 6,274,003; 6,274,032; and 6,365,038.
Lindemuth, P. M., et al., “Improve Desalter Operations” Hydrocarbon Processing, (September 2001) discusses adding dispersant to a desalter to prevent asphaltenes precipitation. This was referred to as desalter instability and can lead to shorter run lengths. Thus this paper suggests deasphalting ahead of the desalter contributes to increased run lengths. The same paper purports that asphaltenes removal upstream of the desalter allows the utilization of crudes that traditionally would present problems in blending. Additionally, a reduction in the load of asphaltenes, salt, and solids challenging the existing desalter is reduced, potentially increasing throughout.
Therefore, notwithstanding existing processes for producing synthetic crude oils, what is needed in the art are processes and systems for: carboxylic acid removal to eliminate requirement of opening naphthenic rings; removal of solids, especially solid fines, and carbon residue; asphaltenes removal and viscosity reduction, i.e. deasphalting; water, salts, and metals removal; and/or removal of heteroatoms as found in naphthenic acids and asphaltenes.
Stable emulsions and asphaltenes cause serious problems for oil refiners. Emulsions complicate refinery operations and lead to operational upsets and production losses. A cost effective way to break emulsions and separate the two liquid phases would be valuable to all companies operating process plants, especially to refining companies. Asphaltenes, the heaviest and most contaminated component of petroleum, in addition to salts, and organic acid (specifically the carboxylic acid family of which naphthenic acids are a part) prevent refiners from using very much of the heavier, and cheaper, grades of petroleum as feedstocks. Cost effective and efficient removal of asphaltenes, salts, and naphthenic acids could upgrade the petroleum, turning the heavy crude into a valuable and lighter refinery feedstock, and potentially reducing our country's dependence on foreign oil.